Preparation And Applications Of Cathode Materials For IT-SOFC

A fuel cell is an energy conversion device with a high efficiency and a lowpollution. It is different from traditional generators, fuel cell has advantages of higherenergy conversion efficiency and lower polluted gases emission over the traditionalgenerator for it is not limited by the Carnot cycle. For IT-SOFC operate at relativelylower temperature between500℃to800℃,it provide more choices of cell materials，facilitate the make technology and stabilize the cell.Thus study and find new kindscathode materials will be very significant to the development of IT-SOFC.In this thesis, Ln0.7Sr0.3Co1-yFeyO3-δ(0.1~0.5)cathode materials were also preparedby co-precipitations method using mixed rare earth but not expensive pure La2O3as theraw materials, and its structure and electrical performance were researched, whichexplored to reduce the cost of SOFC industrialization.The experimental result research shown：The system of Ln0.7Sr0.3Co1-yFeyO3-δcat-hode materials synthesized at1100℃for4h is not single perovskite phase, but twophases with cubic fluorite and perovskite phase presents in it.The ion size factor, thestructure of crystal, the electrovalence influence and so on has shown the Ce in thesystem is main still with+4valence CeO2form existences.The conductivity of the sintered samples was measured by four-probe DC methodfrom room temperature to800℃in air. In low temperature phase, it is almost a straightline according to㏑σT and1/T,the electrical conducting mechanism of LnSCF isp-type small polaron hopping process, the sample electrical conductivity appears themaximum value with the temperature increase. Also has an important reason in the lowtemperature section conductivity rapid fluctuation is Charge disproportionation of Co3+,the Charge disproportionation of Co3+beginning to200℃about, after moreoverbecause introduced substitution ion Sr2+,the response initial temperature also to beable to reduce.So the Ln0.7Sr0.3Co1-yFeyO3system conductivity in300℃beforeincreases with the test temperature fast increases, mainly is because Chargedisproportionation of Co3+produced the extra current carrier.Gradually forms in the high temperature phase oxygen vacancy electric charge compensation, the electriccharge compensates into to the ion compensates primarily, causes in the system thesmall polaron current carrier density to reduce,simultaneously in the system includesCe3+, with temperature increases, Ce3+can consume the partial oxygen vacancy to theCe4+transformation thus has compensated the system electric charge not balancedeffect which the Sr2+doping causes, the material the electric conduction spatial figurewhich appraises by the Co3+ion forms to be less, thus the conductivity reduces.The Fe3+ion radius(0.65)is bigger than the Co3+ionic radius (0.61), causesthe radial direction shrinkage of low Co/Fe proportion sample obviously to be smallerthan the high Co/Fe proportion sample,As a result of the Charge disproportionation ofCo3+, causes the shrinkage rate of change of low Co/Fe proportion sample obviously tobe smaller than the high Co/Fe proportion sample.